1. Field of the Invention
This invention relates to a radiation image read-out method and apparatus. This invention particularly relates to a radiation image read-out method and apparatus, wherein light emitted by a stimulable phosphor sheet is detected with a line sensor.
2. Description of the Prior Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a stimulable phosphor sheet, which comprises a substrate and a layer of the stimulable phosphor overlaid on the substrate. Stimulating rays, such as a laser beam, are deflected and caused to scan pixels in the radiation image, which has been stored on the stimulable phosphor sheet, one after another. The stimulating rays cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted successively from the pixels in the radiation image having been stored on the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal by photoelectric read-out means. The stimulable phosphor sheet, from which the image signal has been detected, is then exposed to erasing light, and radiation energy remaining thereon is thereby released.
The image signal, which has been obtained from the radiation image recording and reproducing systems, is then subjected to image processing, such as gradation processing and processing in the frequency domain, such that a visible radiation image, which has good image quality and can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness, can be obtained. The image signal having been obtained from the image processing is utilized for reproducing a visible image for diagnosis, or the like, on film or on a high resolution cathode ray tube (CRT) display device. The stimulable phosphor sheet, from which residual radiation energy has been released with the erasing light, can be used again for the recording of a radiation image.
Novel radiation image read-out apparatuses for use in the radiation image recording and reproducing systems described above have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 60(1985)-111568 and 60(1985)-236354. In the proposed radiation image read-out apparatuses, from the point of view of keeping the emitted light detection time short, reducing the size of the apparatus, and keeping the cost low, a line light source, such as a fluorescent lamp, a cold cathode fluorescent lamp, or a light emitting diode (LED) array, for irradiating linear stimulating rays onto a stimulable phosphor sheet is utilized as a stimulating ray source, and a line sensor comprising a plurality of photoelectric conversion devices arrayed along the length direction of a linear area of the stimulable phosphor sheet, onto which the stimulating rays are irradiated by the line light source, is utilized as photoelectric read-out means. Also, the proposed radiation image read-out apparatuses comprise scanning means for moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction, which is approximately normal to the length direction of the linear area of the stimulable phosphor sheet.
As for techniques for detecting the light, which is emitted by the stimulable phosphor sheet, with the line sensor, a technique may be considered, in which the emitted light is guided by a cylindrical lens or optical fibers to the line sensor. A technique may also be considered, in which the line sensor is located close to the stimulable phosphor sheet so as to directly receive the emitted light without an optical system intervening between the line sensor and the stimulable phosphor sheet.
However, in cases where the line light source is employed and the emitted light is detected with the line sensor, the light is emitted from the linear area, instead of a point, on the stimulable phosphor sheet. Therefore, in order for an image having high sharpness to be obtained, not only the intensity of the emitted light but also the information concerning the position of light emission must be detected accurately.
Specifically, if the emitted light spreads and impinges upon the line sensor, the light emitted from a single point on the stimulable phosphor sheet will impinge upon a plurality of photoelectric conversion devices constituting the line sensor. Therefore, in such cases, the position, from which the light is emitted, and the intensity of the emitted light cannot be detected accurately. For example, in cases where the light emitted by the stimulable phosphor sheet is guided by a cylindrical lens extending in the length direction of the line sensor, the emitted light is converged with respect to the direction normal to the length direction of the line sensor (i.e., with respect to the direction having a curvature). However, in such cases, the emitted light diverges with respect to the length direction of the line sensor (i.e., with respect to the direction having no curvature). Therefore, a high light collecting efficiency cannot be obtained, and the position from which the light is emitted cannot be detected accurately.
With the technique for guiding the emitted light through optical fibers to the line sensor or the technique for directly receiving the emitted light by the line sensor, the end faces of the optical fibers or the line sensor must be located close to the stimulable phosphor sheet. However, in the image read-out operation, the stimulable phosphor sheet is moved relative to the line sensor. Therefore, it is necessary for a spacing to be left between the line sensor and the stimulable phosphor sheet. The spacing between the line sensor and the stimulable phosphor sheet is markedly larger than the spacing (e.g., approximately 0.1 mm) between adjacent photoelectric conversion devices of the line sensor. Accordingly, as in the cases where the cylindrical lens is employed, a high light collecting efficiency cannot be obtained, and the position from which the light is emitted cannot be detected accurately.
The primary object of the present invention is to provide a radiation image read-out method, wherein an intensity of light emitted by a stimulable phosphor sheet and a position from which the light is emitted are capable of being detected with a high light collecting efficiency and a high spatial resolution, and an image having a high sharpness is capable of being formed from information having been obtained from the detection of the emitted light.
Another object of the present invention is to provide an apparatus for carrying out the radiation image read-out method.
The present invention provides a radiation image read-out method, comprising the steps of:
i) linearly irradiating stimulating rays, which have been produced by a line light source, onto an area of one surface of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) receiving light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet exposed to the linear stimulating rays or from a linear area of the other surface of the stimulable phosphor sheet corresponding to the linear area of the one surface of the stimulable phosphor sheet, with a line sensor comprising a plurality of photoelectric conversion devices arrayed along a length direction of the linear area of the stimulable phosphor sheet, the received light being subjected to photoelectric conversion performed by the line sensor, and
iii) moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction different from the length direction of the linear area of the stimulable phosphor sheet,
wherein the light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet or from the linear area of the other surface of the stimulable phosphor sheet, is converged by a distributed index lens array, which is located between the stimulable phosphor sheet and the line sensor and which comprises a plurality of distributed index lenses arrayed along the length direction of the linear area of the stimulable phosphor sheet.
In the radiation image read-out method in accordance with the present invention, the line sensor should preferably comprise a plurality of the photoelectric conversion devices arrayed along the length direction of the linear area of the stimulable phosphor sheet and along the direction different from the length direction of the linear area of the stimulable phosphor sheet.
Also, in the radiation image read-out method in accordance with the present invention, the distributed index lens array should preferably satisfy the formula:
Nxc3x97{1xe2x88x92cos3(tanxe2x88x921(D/2Lo))}xe2x89xa70.1
in which D represents the diameter of the distributed index lens, Lo represents the working distance of the distributed index lens, and N represents the number of the distributed index lenses falling within the radius of field of the distributed index lens.
Further, in the radiation image read-out method in accordance with the present invention, the working distance of the distributed index lens should preferably fall within the range of 1 mm to 10 mm.
Furthermore, in the radiation image read-out method in accordance with the present invention, the distributed index lens array should preferably have a transmittance of at least 80% with respect to a light component having a wavelength exhibiting the highest intensity among the light components of the light emitted by the stimulable phosphor sheet.
As will be understood from the specification, it should be noted that the term xe2x80x9cmoving a stimulable phosphor sheet with respect to a line light source and a line sensorxe2x80x9d as used herein means movement of the stimulable phosphor sheet relative to the line light source and the line sensor, and embraces the cases wherein the stimulable phosphor sheet is moved while the line light source and the line sensor are kept stationary, the cases wherein the line light source and the line sensor are moved while the stimulable phosphor sheet is kept stationary, and the cases wherein both the stimulable phosphor sheet and the line light source and the line sensor are moved. In cases where the line light source and the line sensor are moved, they should be moved together with each other.
The direction along which the stimulable phosphor sheet is moved with respect to the line light source and the line sensor (i.e., the direction different from the length direction of the exposed linear area of the stimulable phosphor sheet) should preferably be the direction approximately normal to the length direction (i.e., the major axis direction) of the exposed linear area of the stimulable phosphor sheet, i.e. should preferably be the minor axis direction. However, the direction along which the stimulable phosphor sheet is moved with respect to the line light source and the line sensor is not limited to the minor axis direction. For example, in cases where the lengths of the line light source and the line sensor are longer than one side of the stimulable phosphor sheet, the stimulable phosphor sheet may be moved with respect to the line light source and the line sensor along an oblique direction with respect to the direction approximately normal to the length direction of the line light source and the line sensor or along a zigzag movement direction, such that approximately the entire surface of the stimulable phosphor sheet may be uniformly exposed to the stimulating rays.
The line sensor employed in the radiation image read-out method in accordance with the present invention may comprise the plurality of the photoelectric conversion devices arrayed along only the length direction (i.e., the major axis direction). Alternatively, the line sensor may comprise the plurality of the photoelectric conversion devices arrayed along each of the major axis direction and the minor axis direction, which is normal to the major axis direction. In such cases, the plurality of the photoelectric conversion devices may be arrayed in a matrix-like pattern such that they may stand in a straight line along each of the major axis direction and the minor axis direction. Alternatively, the photoelectric conversion devices may be arrayed such that they may stand in a straight line along the major axis direction and in a zigzag pattern along the minor axis direction. As another alternative, the photoelectric conversion devices may be arrayed such that they may stand in a straight line along the minor axis direction and in a zigzag pattern along the major axis direction. As a further alternative, the photoelectric conversion devices may be arrayed such that they may stand in a zigzag pattern along each of the major axis direction and the minor axis direction.
The length of the line sensor, as measured at the light receiving surface, should preferably be longer than or equal to the length of one side of the effective image storing region of the stimulable phosphor sheet. In cases where the length of the light receiving surface of the line sensor is longer than the length of one side of the effective image storing region of the stimulable phosphor sheet, the line sensor may be located obliquely with respect to the side of the effective image storing region of the stimulable phosphor sheet.
The line light source and the line sensor may be located on the same surface side of the stimulable phosphor sheet or on opposite surface sides of the stimulable phosphor sheet. Also, two line sensors may be located on opposite surface sides of the stimulable phosphor sheet. In cases where the line light source and the line sensor are located on opposite surface sides of the stimulable phosphor sheet, the substrate of the stimulable phosphor sheet, or the like, should be formed from a material permeable to the emitted light, such that the emitted light may permeate to the surface side of the stimulable phosphor sheet opposite to the surface on the stimulating ray incidence side.
The present invention also provides an apparatus for carrying out the radiation image read-out method in accordance with the present invention. Specifically, the present invention also provides a radiation image read-out apparatus, comprising:
i) a line light source for linearly irradiating stimulating rays onto an area of one surface of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) a line sensor for receiving light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet exposed to the linear stimulating rays or from a linear area of the other surface of the stimulable phosphor sheet corresponding to the linear area of the one surface of the stimulable phosphor sheet, and performing photoelectric conversion of the received light, the line sensor comprising a plurality of arrayed photoelectric conversion devices, and
iii) scanning means for moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction different from a length direction of the linear area of the stimulable phosphor sheet,
wherein a distributed index lens array, which comprises a plurality of distributed index lenses arrayed along the length direction of the linear area of the stimulable phosphor sheet, is located between the stimulable phosphor sheet and the line sensor in order to converge the light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet or from the linear area of the other surface of the stimulable phosphor sheet.
In the radiation image read-out apparatus in accordance with the present invention, the line sensor should preferably comprise a plurality of the photoelectric conversion devices arrayed along the length direction of the linear area of the stimulable phosphor sheet and along the direction different from the length direction of the linear area of the stimulable phosphor sheet.
Also, in the radiation image read-out apparatus in accordance with the present invention, the distributed index lens array should preferably satisfy the formula:
Nxc3x97{1xe2x88x92cos3(tanxe2x88x921(D/2Lo))}xe2x89xa70.1
in which D represents the diameter of the distributed index lens, Lo represents the working distance of the distributed index lens, and N represents the number of the distributed index lenses falling within the radius of field of the distributed index lens.
Further, in the radiation image read-out apparatus in accordance with the present invention, the working distance of the distributed index lens should preferably fall within the range of 1 mm to 10 mm.
Furthermore, in the radiation image read-out apparatus in accordance with the present invention, the distributed index lens array should preferably have a transmittance of at least 80% with respect to a light component having a wavelength exhibiting the highest intensity among the light components of the light emitted by the stimulable phosphor sheet.
With the radiation image read-out method and apparatus in accordance with the present invention, the light, which is emitted by the stimulable phosphor sheet when the stimulable phosphor sheet is exposed to the stimulating rays produced by the line light source, is converged by the image, forming optical system (i.e., the distributed index lens array), which is located in the optical path between the line light source for linearly irradiating the stimulating rays onto the stimulable phosphor sheet and the line sensor for receiving the emitted light and photoelectrically converting it. The image forming optical system has object points on the light emission surface of the stimulable phosphor sheet has image points on the light receiving surface of the line sensor. Therefore, the information (i.e., the image carrying the information) representing the intensity distribution of the emitted light on the light emission surface of the stimulable phosphor sheet can be directly formed on the light receiving surface of the line sensor. Accordingly, even if the optical system for collecting the light emitted by the stimulable phosphor sheet is located at a spacing from the stimulable phosphor sheet, the intensity of light emitted by the stimulable phosphor sheet and the position from which the light is emitted can be detected with a high light collecting efficiency and a high spatial resolution, and an image having a high sharpness can be formed from image signal information having been obtained from the detection of the emitted light.
Also, with the radiation image read-out method and apparatus in accordance with the present invention, the line sensor may comprise the plurality of the photoelectric conversion devices arrayed along the length direction of the linear area of the stimulable phosphor sheet and along the direction normal to the length direction of the linear area of the stimulable phosphor sheet. In such cases, if the line width of the light emitted by the stimulable phosphor sheet, which line width is formed on the light receiving surface of the line sensor, is larger than the light receiving width of each photoelectric conversion device, the line sensor as a whole can receive the emitted light over the range of the large line width of the emitted light, which line width is formed on the light receiving surface of the line sensor. As a result, the light collecting efficiency can be enhanced even further.
Further, with the radiation image read-out method and apparatus in accordance with the present invention, wherein the distributed index lens array satisfies the formula shown below, the light collecting efficiency of the distributed index lenses can be kept to be at least 10%.
Nxc3x97{1xe2x88x92cos3(tanxe2x88x921(D/2Lo))}xe2x89xa70.1
in which D represents the diameter of the distributed index lens, Lo represents the working distance of the distributed index lens, and N represents the number of the distributed index lenses falling within the radius of field of the distributed index lens.
Furthermore, with the radiation image read-out method and apparatus in accordance with the present invention, wherein the working distance of the distributed index lens falls within the range of 1 mm to 10 mm, the movement of the stimulable phosphor sheet with respect to the line light source and the line sensor is not obstructed. Also, the light collecting efficiency can be prevented from becoming low, and an image having a high sharpness can be obtained.
Also, with the radiation image read-out method and apparatus in accordance with the present invention, wherein the distributed index lens array has a transmittance of at least 80% with respect to the light component having the wavelength exhibiting the highest intensity among the light components of the light emitted by the stimulable phosphor sheet, a desired light collecting efficiency can be kept, and an image having a high sharpness can be obtained.